1. Field of the Invention
The present invention relates to a magnetic recording apparatus and in particular, to a magnetic recording apparatus for recording and reproducing data with comparatively high density. The present invention also relates to a head error detection apparatus for detecting an error caused by a magnetic head for writing and in particular, to a program product for detecting a head error.
2. Description of the Related Art
Conventionally, a magnetic recording apparatus comprises a head drive circuit including a head error detection circuit for detecting a head error such as a write magnetic head disconnection and a short-circuit.
In general, the head error detection circuit detects a voltage level of reverse electromotive force pulse generated at a head current switching and compares the value detected with a reference value. When a head error such as disconnection and short-circuit is caused, the voltage level of the reverse electromotive force pulse does not reach the reference value. Upon detection of this small voltage, the error detection circuit generates a fault pulse signal, which causes a magnetic recording apparatus to enter an interrupt mode in which no data recording is carried out.
The head error detection circuit executes a write unsafe (WUS) check. A WUS check circuit has an inherent frequency characteristic and cannot operate in response to a frequency above a predetermined frequency band. Moreover, WUS check circuits of an identical type may differ in the frequency characteristic. To cope with this, in general, a head portion of a data area contains a signal of a single frequency, i.e., xc2xd or ⅓ of the maximum frequency, and the area where this signal is written serves as an object of the WUS check. This area to be checked will be referred to as a xe2x80x9cWUS check areaxe2x80x9d.
Explanation will be given of a conventional head error detection circuit disclosed in Japanese Patent Publication (Unexamined) No. A-4-313864. In this circuit a recording current is reduced because an apparatus using this circuit has a high efficiency, low-floating head. This results in a low frequency data write which is normal but regarded as an error. To cope with this, the aforementioned head detection circuit changes the area subjected to the write unsafe (WUS) check. This prevents a malfunction and enables correct execution of the WUS check.
These years, the magnetic recording apparatus has increased its data transfer rate and write frequency, which in turn requires strict conditions of overwrite and non-linear bit shift. Accordingly, depending on the recording frequency, the head error detection circuit has a higher sensitivity, which increases the frequency of malfunctions caused by a noise overlaid in a power source and grinding line or inductance. If the head error detection circuit operates incorrectly, an error is detected and a write operation is interrupted even when the apparatus is in a normal state.
It is therefore an object of the present invention to provide an improved magnetic recording apparatus capable of preventing a malfunction to decide a normal apparatus as an error.
Another object of the present invention is to provide a magnetic recording apparatus capable of carrying out a stable recording operation, irrespective of the recording frequency change.
In the magnetic recording apparatus according to the present invention, when a head error is detected, a data write is retried with a recording frequency different from a normal recording frequency. More specifically, the data write is retried with a recording frequency higher or lower than the normal recording frequency. If no error is detected in this retrial, a write operation is resumed in a data area. This prevents incorrect an decision that the apparatus which should be normal is not in a normal state. Moreover, it is possible to carry out, at a write check or apparatus rise, a data write with a recording frequency different from a normal recording frequency, irrespective of a head error.